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An ATSB preliminary factual report into an electrical system failure involving a Boeing 747-400 near Bangkok on 7 January 2008 indicates that the event was less serious than first reported.

The aircraft, with 346 passengers and 19 crew on board, was being operated on a scheduled service between London and Bangkok. When the aircraft was at about 21,000 feet on descent to Bangkok Airport, the customer service manager notified the flight crew that a substantial water leak had occurred in the forward galley. Over the following 12 to 13 minutes, cockpit indications showed a number of electrical bus and system failures that indicated alternating current (AC) buses, 1, 2 and 3 were not powered. The status of AC bus 4 appeared normal and some systems were powered by batteries.

The captains primary flight display, navigation display, and some other instruments were available in a degraded mode and the crew conducted an uneventful approach and landing in day visual meteorological conditions.

Post-flight inspections identified a minor water leak in the forward galley sink drain and that an ice drawer drain was blocked. That inspection also found cracks in a fibreglass drip shield located above an electrical component rack in the aircraft's main equipment centre, as well as evidence of dark liquid stains on the shield. Further inspection found that a ribbon heater on a drain line leading to the forward grey water drain mast was inoperative, and that a length of hose on the drain line at that location was split.

On 11 January 2008, the aircraft manufacturer issued a Multi Operator Message to operators of 747-400 series aircraft, containing advice and instructions for the inspection and repair of main equipment centre drip shields. The manufacturer is preparing an inspection and repair alert service bulletin on the same subject that is scheduled for release by May 2008.

In addition to conducting fleet-wide inspections and, where necessary, repairs to drip shields and drainage systems, the aircraft operator issued a Cabin Standing Order and a Flight Standing Order requiring cabin and flight crews to identify, treat and report abnormal water accumulation in galley areas.

The event involves complex systems and a wide-ranging investigation is continuing with the cooperation and assistance of local and international agencies, the aircraft manufacturer and the operator. Given the complex nature of the investigation, the ATSB is not able to comment further to the text contained in the preliminary report. Provision of analysis and findings in relation to the circumstances of this incident (which may be further revised) will be provided in the final report. In addition, the ATSB will immediately communicate any need for urgent safety action should that become evident during the investigation.

Copies of the report can be downloaded from the ATSBs internet site at www.atsb.gov.au

Media contact: 1800 020 616
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Last update 01 April 2011